In the recycling of metals, aluminum scrap pieces are melted for treatment and processing. A large portion of the aluminum scrap pieces are thin walled as a result of the mechanical shaping action from which they were formed. Melting thin walled scrap pieces is difficult because rapid submergence in molten metal is severely hampered since thin walled scrap pieces tend to float on molten metal. Unfortunately, extended exposure to the hostile atmosphere in a traditional melting furnace results in extremely high oxidation loss.
In a typical melting operation, a melting furnace is provided with an enclosed hearth and a connected open sidewell. Usually the sidewell is divided into a pump well and a melting bay. A pump or other molten metal flow inducing apparatus is positioned in the pump well and pumps molten metal from the hearth to the melting bay. Sometimes the melting bay is further divided into a chargewell and a drosswell. Metal scrap pieces are fed into the melting bay, particularly the chargewell.
A variety of apparatus have been used in the melting bay, specifically in the chargewell, to facilitate the submergence of the scrap metal below the surface of the molten metal bath. Three major types of systems exist. The first type includes mechanical systems constructed primarily of a rotor that creates a molten metal flow from the top surface. The second type of system uses a mechanical device to physically push the scrap below the melt surface (elephant feet/well-walkers). The third type of system relies on the shape of the chamber to create a metal flow that submerges scrap pieces in the chargewell. Particularly, the flow of molten metal into the chargewell is manipulated in such a manner to achieve a vortex that draws chips from the top surface into the bath.
In known systems that rely on the shape of the chamber to create a metal vortex flow, the chargewell is typically made of a refractory material. Significant stress is imparted on the chargewell because the temperature of the molten metal inside of the chargewell is very high and the lower portion of the chargewell is typically submerged in the furnace while the upper portion of the charge well is not. This can create a large temperature gradient between the refractory material in the lower portion of the chargewell and the refractory material in the upper portion of the chargewell. In addition, the forces created by the high speed metal circulation impart stresses on the chamber walls. Since the chamber is often an integral component of the furnace, repair of the walls, or in fact even cleaning, can be a difficult and expensive undertaking, particularly in the form of furnace downtime.